function ajax(url,sccuessFn,failureFn){
  var xhr = new XMLHttpRequest()
  xhr.onload = function () {
    sccuessFn(xhr.responseText)
  }
  xhr.onerror = function(){
    failureFn(xhr.responseText)
  }
  xhr.open("get", url, true)
  xhr.send()
}

function $(dom){
  return document.querySelectorAll(dom)
}
